In modern internal combustion engines, devices for variably adjusting the control times of gas exchange valves are used in order to be able to variably configure the phase relationship between the crankshaft and camshaft in a defined angle range between a maximum early position and a maximum late position. For this purpose, the device is integrated into a drivetrain via which a torque is transmitted from the crankshaft to the camshaft. Said drivetrain may, for example, be realized as a belt drive, chain drive or gearwheel drive.
The device comprises at least two rotors which are rotatable relative to one another, with one rotor being drive-connected to the crankshaft and with the other rotor being rotationally fixedly connected to the camshaft. The device comprises at least one pressure space which is divided by means of a movable element into two pressure chambers which act counter to one another. The movable element is operatively connected to at least one of the rotors. By means of a supply of pressure medium to or a discharge of pressure medium from the pressure chambers, the movable element is displaced within the pressure chamber, thereby effecting a targeted rotation of the rotors relative to one another and therefore of the camshaft relative to the crankshaft.
Here, one of the pressure chambers of each pressure space acts as a lead chamber and the other acts as a lag chamber. By means of a supply of pressure medium to the lead chambers with a simultaneous discharge of pressure medium from the lag chambers, the rotor which interacts with the camshaft is rotated relative to the rotor which interacts with the crankshaft in the direction of a maximum early position. By means of a supply of pressure medium to the lag chambers with a simultaneous discharge of pressure medium from the lead chambers, the rotor which interacts with the camshaft is rotated relative to the rotor which interacts with the crankshaft in the direction of a maximum late position.
The supply of pressure medium to and the discharge of pressure medium from the pressure chambers are controlled by means of a control unit, generally a hydraulic directional control valve (control valve). The control unit is in turn controlled by means of a regulator, which, by means of sensors, determines the actual position of the camshaft in the internal combustion engine and compares said actual position with a nominal position, which is dependent, in particular on the engine speed and the load state of the internal combustion engine. If a difference is detected between the two positions, a signal is transmitted to the control unit which adapts the pressure medium flows to the pressure chambers to said signal.
To ensure the functioning of the device, the pressure in the pressure medium circuit of the internal combustion engine must exceed a certain value. Since the pressure medium is generally provided by the oil pump of the internal combustion engine and the provided pressure therefore rises synchronously with the rotational speed of the internal combustion engine, below a certain rotational speed, the oil pressure is still too low to be able to selectively vary or hold the phase position of the rotors. This may be the case, for example, during the starting phase or during the idle phase. During said phases, the device would vibrate in an uncontrolled manner, which would lead to increased noise emissions, increased wear, unsettled running and increased emissions of the internal combustion engine. To prevent this, it is possible to provide mechanical locking devices which rotationally fixedly couple the two rotors to one another during the critical phases of the internal combustion engine, with it being possible for said coupling to be eliminated by virtue of the locking device being charged with pressure medium.
A device of said type is known for example from U.S. Pat. No. 6,439,181 B1, in which an outer rotor is rotatably mounted on an inner rotor which is designed as an impeller, with a plurality of pressure spaces being formed between the outer rotor and inner rotor, which pressure spaces are each divided by means of the vanes into two pressure chambers which act counter to one another. Also provided are two rotational angle limiting devices, with one rotational angle limiting device, in the locked state, restricting a relative rotation of the rotors with respect to one another to an angle range between a maximum late position and a defined central position (locking position). The other rotational angle limiting device, in the locked state, permits a rotation of the inner rotor relative to the outer rotor in an angle range between the maximum early position and the central position. If both rotational angle limiting devices are in the locked state, then the phase position of the inner rotor relative to the outer rotor is restricted to the central position (locking position). Also provided in said embodiment is an auxiliary control mechanism, which, in the locked state, restricts the relative phase position of the inner rotor with respect to the outer rotor to an angle range between a central late position and the maximum early position.
In the locking position, in each case one locking plate, which is arranged in a receptacle of the outer rotor with a force in the direction of the inner rotor, engages in each case into a locking depression formed opposite on the inner rotor, as a result of which the respective rotational angle limiting device passes from the unlocked into the locked state. Each of the rotational angle limiting devices can be moved from the locked into the unlocked state by virtue of the respective locking depression being charged with pressure medium. Here, the pressure medium forces the locking plates back into their receptacle, as a result of which the mechanical coupling of the inner rotor to the outer rotor is eliminated.
The charging of the locking depressions with pressure medium takes place in each case via a connecting line to the pressure chambers. Here, the associated locking depressions of the two rotational angle limiting devices, which in the locked state restrict the phase position of the inner rotor with respect to the outer rotor to the central position, are supplied with pressure medium, in each case, via one of the pressure chambers which act as lag and as lead chambers respectively, while the locking depression, which corresponds to the auxiliary control mechanism, likewise communicates with one of the pressure chambers which act as lag chambers.
A disadvantage of the illustrated embodiment is the fact that the rotational angle limiting devices and the auxiliary control mechanism are controlled by means of the pressure prevailing in the pressure chambers. During an engine start, it is possible, with rising pressure medium pressure in the pressure chambers, for the device to inadvertently unlock and for the phase relationship between the crankshaft and the camshaft to be adjusted in the direction of the maximum late position as a result of the friction torques acting on said camshaft. Furthermore, in said embodiment, a preload component is required in order, during an engine start of the internal combustion engine in a maximum or in a central late position, to permit an adjustment into the locking position by means of the action of the preload force of the preload component counter to the friction torques acting on the camshaft. Here, the device arrives in the locked state only after a time delay, with the inner rotor performing periodic oscillating movements relative to the outer rotor on account of the alternating torques acting on the camshaft from the reaction forces from the actuation of the gas exchange valves. This leads to increased noise emissions, increased wear, unsettled running and increased emissions of the internal combustion engine.
Provision is also made in said embodiment for all of the pressure chambers and all of the locking depressions to be connected to a tank during the stopping and starting phases of the internal combustion engine, which leads to an insufficient supply of lubricant to the device and, therefore, to increased wear. This situation is also disadvantageous, since, before an adjustment of the device, the emptied pressure chambers must be filled with pressure medium, and the adjusting process is therefore subject to a time delay.